OCTANE requirement increase and combustion-chamber deposit weights are lower with the new high V.I. oils than with conventional SAE 20–20W oil containing bright stock, according to the authors.
Fuel economy at 30 mph constant speed is slightly better, they found, using the new high V.I. oils than it is when a 100 V.I. lubricant of equivalent Saybolt viscosity at 210 F is used. The high V.I. oils seem to have no advantage in normal suburban highway driving.
Intake-valve deposits are heavier with the new high V.I. oils than with conventional lubricants. Whether these deposits are due to the V.I. improver or to failure of the volatile base stocks to wash the deposits from the valve backs is not known.